For half a century, synaptic plasticity in the mammalian brain has been the leading paradigm for the study of learning and memory. The olfactory bulb has been supposed to be a site for certain forms of olfactory memories, and the mitral-granule cell reciprocal synapse is a prominent synapse in the bulb. The mitral-granule synapse is worthy of study for three reasons. First, it mediates lateral and reciprocal inhibition in the olfactory bulb, which shape the responses of the output neurons of the olfactory bulb to odor stimuli. Second, the interplay of synaptic dynamics of excitation and inhibition may produce a complex response to patterns of stimuli. Third, the reciprocal arrangement of this synapse presents an opportunity for the direct interaction of pre- and postsynaptic processes. Therefore, the mitral-granule cell reciprocal synapse is an excellent site at which to study the circuits and mechanisms that underlie learning in the mammalian brain. Whole-cell recordings will be made from mitral and granule cells in the olfactory bulb slice preparation. These studies will (1) characterize short- and longterm plasticity in both the excitatory and inhibitory directions over time courses corresponding to odor sampling in vivo, and (2) use pharmacological manipulations, calcium buffers and mutant mice to characterize the mechanisms of the plasticity.